Attc ventilation gap regs.

Calibos

Not sure of the correct terminolgy but most of our bedrooms have semi vaulted ceilings. What I mean is the majority of the ceiling is flat and about 3ft higher than the exterior walls with about a 30deg slope from the ceilings to exterior wall around the periphery.

Renovation builder in 2010 insulated the attic above with fiberglass rolls. While he did imstall a vapour proof barrier on the warm side everywhere he just stuffed fiberglass rolls into the angled vaulted part of the ceiling completely filling the 100mm rafter depth totally blocking vemtilation from the eaves/soffits into the attic. ie. he did not fit vent cards. I plan to remedy this (amongst other things discussed in other threads of mine)

I've been googling vent cards. Came across black plastic ones. While they do look like they create a 50mm deep open area, they dont span rafter to rafter in promo images that look like the rafters are about 16in on center. So my question is wherher the regs specify 50mm deep gap no matter the width of the gap between rafters, or if the regs simply stipulate a square inch type of area. What I mean is can the ventilation gap be 25mm deep but span the full 16in between rafters as opposed to 50mm deep but only spanning haf the width between rafters? Hope I'm explaining myself well enough.

Anyway, I had an idea for retrofitting insulation with ventilation gap without pulling down Victorian ceilings or lifting roof slates. ie. Pull out fiberglass rolls from the vaulted area and push back down 100mm insulation board (100mm deep rafters) but before install routing out the required ventilation gap from the foam. No need for tricky vent card installation.

The question is whether I route out something like an 8-10in wide 50mm deep channel in the foam insulation board or a 25mm deep channel nearly the full width of the 16in wide board with just a lip each side to maintain spacing.

Calahonda52

Fitting a few roof tile vents above and below the sloped area would be a lot easier than what you propose.
Fine in theory but a non runner in practice for tight fitting insulation

Calibos

Calahonda52 wrote: »

Fitting a few roof tile vents above and below the sloped area would be a lot easier than what you propose.
Fine in theory but a non runner in practice for tight fitting insulation

Ah! I think I've fallen into the trap of thinking about the cold attic space in question similarly to the the vertically offset attic conversion in the other 1/3rd of the roof space. That Room has a fully vaulted ceiling.

So while in the fully vaulted attic conversion bedroom we want the 50mm ventilation gap between felt and insulation from Eaves/Soffit to Ridge, for the cold attic space we actually don't need to worry about ventilating from the eaves/soffit through the insulation in the semi vaulted section. We simply need to ventilate as low as possible in the attic space itself and up high.

Surely these are suitable then with no need for lifting slates to fit Vent tiles? I'll need to fit Ridge Vent tiles for the Attic conversion bedroom ventilation retrofit anyway so will fit a few to the Ridge up that end of the roof while I'm at it.

I've safe accessand working environment for the Ridge and leeward side of the roof.

My only mild concern now simply relates to the insulation packed into the semi vaulted sections and wind from the Soffit vents blowing/sucking the warm trapped out of it. That was my rationale for the insulation board idea because wind can't blow the trapped heat out of it. I know from the attic conversion where the Eaves storage area along the exterior wall side of the room has a serious draught problem from the eaves/soffits. Where the vapour barrier is torn or I've pulled it away for inspection, it literally flaps in the wind despite insulation roll stuffed between the rafters, so I'm assuming the insulation in the cold attic is as easily blown through by the wind.